Give priority to supporting materials that are backed by credible evidence. Whether you are relying on examples, testimony, statistics, or other types of support, these materials will be most effective when they are proven. For example, in a speech on the hazards of texting while driving, the statement that the average “eyes-off-the-road time” for sending a text message is equivalent to “traveling the length of a football field at 55 miles per hour without looking at the roadway” is a compelling analogy. But it will be a much more believable one if you identify the author of the study—the Virginia Tech Transportation Institute.21 If you merely assert this fact without proof or attribute it to a Web site of uncertain authorship, the analogy will be much less convincing.
